BRICS is less about alliances, in fact the UAE and Iran are enemies to the level of the US and Russia. It's more about reducing the influence of Western sections on global politics. Basically anyone not reliant on the West financially would benefit from joining BRICS since it reduces the leverage the West has over them.

ETA: it's a similar concept to OPEC where many countries are outright enemies.

BRICS is a trading bloc not a military alliance.

Also, BRICS is rumored to be starting its own currency and we have already seen stuff like Sri Lanka using rupees to deal with its economic crisis. That's going to be very attractive to some countries hence the clamour to join.